setRotation() does not react so setTransformationOriginPoint()

Hello everybody,
first of all thank you to the whole community here. Because I'm pretty new to Qt/ (C++ in general) I appreciate all the comprehensible explanations for common beginner-problems on here.
Unfortunately I struggle with a pretty simple problem since days and can't work around it. I'm trying to rotate a QGraphicsPixmapItem around it's center, but although I'm redefining the origin point to the center, the function setRotation() still rotates around the point (0,0). What's even more weird is, that unlike setRotation() the setPos() function accepts the new origin point. In the following code I've stripped down the problem to the bare minimum and hope someone might find my mistake.

Hello @mrjj, thanks a lot for the quick reply. Somehow the scaling of my picture was messing up the redefiniion of my origin point (and also redefining the origin point in the wrong directions). I was scaling a 2500x2500px picture down to 100x100px, which somehow must have messed up my values "xc" and "yc". After rescaling the source picture externaly it worked perfectly (even if I still scale the picture down internally from 200x200 to 100x100. A scaling factor 4% apperently was to much though).
Again, thanks a lot for your code example, it helped a lot. Also thanks to @Pl45m4
Best regards

@mrjj
It's actually the front-end visulizitation of a simulated "real" autonomous robot-factory, transporting RFID-chips to different scanners simulating the production. This is what the final project of the class from the previous semester looked like. https://www.youtube.com/watch?v=X2C8Ajh29ak

@mrjj
We do have a camera system installed on the ceiling which is tracking the markers on the back of the robots, but we also keep track of the driven distances by measuring the wheel rotations. Those to datasets are somehow combined (no clue how the other group is doing that) and given to us as positioning feedback for visulization purpose.
If my group also has the spare time to make a video I'll post on here :) (Due is around december though)